1. Field of the Invention
The present invention relates to a substrate transfer apparatus and a substrate transfer method, and more particularly to a substrate transfer apparatus that transfers a substrate in order to perform, for example, a plasma process onto a surface of the substrate, which is a plate-like subject to be processed having a flat plate shape, and a substrate transfer method for transferring a substrate by using the substrate transfer apparatus.
2. Description of the Related Art
When a semiconductor thin film is formed on a surface of a substrate that is a subject to be processed having a flat plate shape, a plasma processing apparatus employing a plurality of vacuum chambers has widely been used. In the plasma processing apparatus described above, at least one of the plurality of vacuum chambers is generally specified as the vacuum chamber for a plasma process for performing the plasma process onto the surface of the substrate. Further, the plasma processing apparatus generally includes a transfer apparatus for transferring the substrate among the plurality of vacuum chambers.
As the transfer apparatus, there has been known an apparatus of a floating-type transfer system. In the apparatus of the floating-type transfer system, a guide plate for mounting a substrate is provided to each of vacuum chambers, and the substrate is mounted on the guide plate. Then, the substrate is floated from the guide plate by means of a floating gas in the vacuum chamber. The floated substrate is transferred to the adjacent vacuum chamber along the guide plate.
Specifically, the substrate transfer apparatus of the floating-type transfer system includes a floating-transfer guide plate provided at each vacuum chamber and provided with a plurality of floating-gas ejecting holes, and a gas supplying source for supplying the floating gas to the respective guide plates. Since the floating gas is ejected from the gas ejecting holes of the guide plate, the substrate is floated from the guide plate, and then, the floated substrate is transferred along the guide plate among the plurality of vacuum chambers due to external force.
Apparatuses disclosed in Japanese Unexamined Utility Model Publication No. 61-178725 and Japanese Unexamined Patent Publication No. 7-228342 have been also known, for example, as the substrate transfer apparatus utilizing the transfer system described above.
The substrate transfer apparatus of the floating transfer system described above includes, for example, a horizontally extending transfer arm that can move up and down for transferring a rectangular substrate among a plurality of vacuum chambers, and a transfer drive unit for transferring/moving up/down the transfer arm in a transfer direction and in a vertical direction.
However, there arise problems described below in the substrate transfer apparatus, of the substrate transfer apparatuses having the transfer arm and the transfer drive unit, in which the substrate is not directly mounted on the guide plate, but the substrate is mounted through a tray placed on the guide plate in order to protect the surface of the substrate.
The tray has to be formed to have an area larger than the area of the substrate to be mounted thereon. In order to achieve this, the tray generally has a rectangular planar shape, and a portion close to a side edge and a portion close to an end edge are formed to project, whereby the length of the long side and the length of the short side are larger than those of the substrate. The reason is because it is necessary to form a plurality of fitting holes along the transfer direction, with which a suspending leading portion of the transfer arm is releasably fitted by an ascending/descending movement, at the portions close to the side edge of the tray on which the substrate is mounted.
When the tray and the transfer arm are configured as described above, it is not so easy to achieve positioning of the fitting holes on the tray and the leading portion of the transfer arm upon the fitting, unless the tray is correctly placed on a predetermined portion with respect to the guide plate. This provides non-smooth fitting, which entails a trouble related to the transfer.
When the tray and the transfer arm are configured as described above, and further, the guide plate has incorporated therein a heater for heating the substrate, wherein the heater is formed to have the width almost the same as that of the substrate, the problem described below arises. Specifically, because the portion close to the side edge of the tray projects from the side edge of the guide plate, the difference in a temperature distribution occurs between a portion of the tray facing the heater and a portion of the tray projecting from the heater, when the substrate is heated by the heater. Due to the difference in the temperature distribution, the tray might be curved upwardly at the portion close to the side edge, with the result that a film-forming process for manufacturing a semiconductor thin film onto the surface of the substrate is not satisfactorily performed, or the trouble related to the transfer might occur.